Marine propellers



1968 E. s. SH'IRET MARINE PROPELLERS 5 Sheets-Sheet 1 Filed May 10, 1967Nov. 26, 1968 E- s. SHIRET 3,412,809

MARINE PROPELLERS Filed May 10, 1967 3 Sheets-Sheet 2 United StatesPatent 3,412,809 MARINE PROPELLERS Edmund Stanley Shiret, Catford,England, assiguor to Stone Manganese Marine Limited, London, England, aBritish company Filed May 10, 1967, Ser. No. 637,484 Claims priority,application Great Britain, May 17, 1966, 21,790/ 66 1 Claim. (Cl.170-173) ABSTRACT OF THE DISCLOSURE A keyless marine propeller assemblycomprising a driving shaft within a boss of the propeller, characterisedin that the shaft is tapered but composed of three radially or angularlyrelatively offset portions, of which the fore and aft portions havetheir axes aligned with the axis of the main portion of the shaft andthe centre portion is offset. Transitional zones between the portionslie in lightening chambers in the boss.

This invention relates to marine propellers. More particularly theinvention is concerned with an improved construction of a marinepropeller and shaft causing the propeller and propeller shaft to bemanufactured With less possibility of failure and to give more reliableservice.

At present, it is standard practice for a marine propeller to be fittedto a shaft, circular in cross-section, on a taper with a key and keywayto ensure that there is no angular movement. The propeller is driven uphard on the taper and is held there by means of a conventional nut.

The known method has the disadvantage that the cutting of a keyway ofthe shaft causes local stress raisers leading under certain conditionsto shaft failure, particularly in large single screw vessels where theshaft torque is high.

An object of the invention is to overcome the abovementioneddisadvantage and provide an improved propeller construction whichobviates the necessity for a key and keyway.

The invention consists in a marine propeller assembly comprising adriving shaft within a boss of the propeller, the shaft being taperedbut composed of two or more radially or angularly ofiset portions.

One object of the invention is to allow the propeller to be driven bythe method of a crank, which is essentially a stepped or offset shaft.Once the shaft and propeller are in position further application oftightening force, e.g., by a hydraulic nut, such as a pilgrim nut,produces greater grip between the mating surfaces.

It is normal practice for the coupling between a shaft and a propellerto be capable of taking torques equal to about three times the nominalmaximum torque to provide a margin of safety against shock loading. Ithas been found advantageous for the propeller according to the inventionto be driven up onto the shaft so that the frictional grip arising fromthe interference is at least capable of transmitting the nominal maximumtorque and preferably 50% more. In this way, small angular relativemovements are virtually prevented and the possibility of frettingcorrosion is substantially eliminated.

It is necessary to imprint on the after face of the shaft and the afterface of the boss, some indication of the correct position at which thepropeller is to be fitted on the shaft. At this particular position thebOSs is fitted by pushing it axially on the shaft. If the boss is fittedon the shaft at some other position then the boss will move angularly asit proceeds axially along the boss until he Patented Nov. 26, 1968correct position is reached when the indicator on the shaft and bosswill be in line. In the reverse process of unshipping the propeller, theboss moves only axially down the shaft.

At the juncture of the offset shaft portions it is not necessary to stepthe bore to correspond since it is envisaged that these positions willbe within the lightening chamber. The amount of axial offset will onlybe very small, and a smooth transition can be made from one part of theshaft to another in this region of the lightening chamber.

In one form, the shaft within the bore is composed of two sections only,both tapered, although it is permissible within the scope of thisinvention to have any number of portions each offset, with or withouttaper, provided that the said portions are enclosed by a taperedenvelope within the bore.

The invention will be further described with reference to theaccompanying diagrammatic drawings, in which:

FIGURE 1 is a sectional view of the shaft end with a propeller bossthereon, incorporting one form of the invention (omitting the propellerblades);

FIGURE 2 is an end elevation showing the relative radial positions ofthe portions of the shaft;

FIGURE 3 is a view similar to FIGURE 1 (omitting the threaded portion atthe aft end of the shaft) of a modified embodiment;

FIGURE 4 is a sectional View at IV-IV of FIGURE 3 showing the shaftonly;

FIGURE 5 is a view similar to FIGURE 3 of a further modified embodiment;and

FIGURES 6 and 7 are sectional views at VIVI and VII-VII respectively ofFIGURE 5, showing the shaft only.

In FIGURES 1 and 2 the eccentricities are shown somewhat exaggerated forclarity of illustration.

The propeller boss 1 has a forward face 2 and a complex tapered boretherein co-operates with a mating tapered end of a shaft 3. The boreincludes a lightening chamber 4. The boss is held on the shaft by a nut5.

The axis of the propeller shaft 3 is shown at 6. The visible end part ofthe shaft is somewhat offset from this axis for the purpose ofmaintaining a dynamic balance of the whole assembly about the axis 6.

The tapered end of the shaft comprises a forward portion 7 and an aftportion 8 having their axes 9 and 10 offset to opposite sides of theaxis 6. The forward and aft ends of the part 7 are shown at 11 and 12respectively, while the forward and aft ends of the portion 8 are shownat 13 and 14 respectively. It will be seen that the ends 12 and 13 areboth in the lightening chamber 10 when the propeller is located in theshaft.

While the axes 9 and 10 have been shown offset on opposite sides of theaxis 6 for balance of the assembly, it may be simpler to align the axis9 with the axis 6 and to provide compensation for the offset of the axis10 by the form of the lightening chamber, or otherwise, e.g., in thebalance of the propeller.

This is shown in FIGURES 3 and 4 wherein the sharp discontinuity at theends 12 and 13, which was only shown to illustrate the invention clearlyand is clearly unacceptable from a practical point of view, is replacedby a transitional zone 15, wherein the radius of the shaft is firstprogressively reduced from one side, as illustrated at 16, and thenprogressively increased from the opposite side, as illustrated at 17.The areas 16 and 17 are contiguous longitudinally and the whole zone 15lies within the lightening chamber 4.

FIGURES 5 to 7 show a further embodiment in which there are threesections 21, 22 and 23 radially offset from the adjacent section orsections. The sections 21 and-23 are each coaxial with the shaft 3itself and the section 22 has an axis 24 offset from the shaft axis 6.There is a lightening chamber 4a or 4b at each transition zone 25 and26, and as shown, the transition takes place progressively over acomparatively short length, and from one side only in each transitionzone.

Various other modifications may be made within the scope of theinvention. For instance, the sections have all been shown radiallyoffset, i.e. at 180, but this is only a special case of angularoflsetting, which is also within the scope of the invention.

I claim:

1. A keyless marine propeller assembly comprising a propeller having aboss and a driving shaft having an end inserted in the boss of thepropeller, the boss including at least two lightening chambers; theassembly having the improvements that the shaft end is tapered andcomposed of three portions angularly offset in relation to each other,the three portions being a forward portion and an aft p rtion eachcoaxial with the main portion of the shaft and a middle portion offsetin relation thereto, the shaft end further comprising short transitionalzones between adjacent portions, each of the transitional zones lying inone of the lightening chambers.

References Cited UNITED STATES PATENTS 612,302 10/1898 Ballot 170l73 X1,358,430 11/1920 Faehrmann 170-l73 X 1,402,463 1/ 1922 Wilson.3,228,482 1/1966 Bunyan 170-173 EVERETTE A. POWELL, JR., PrimaryExaminer.

